The present invention provides a process for separating low molecular weight oligomers of a film forming resin utilizing the combination of a static mixer and a liquidxe2x80x94liquid centrifuge. The low molecular weight oligomers are useful in enhancing the photospeed of a photoresist composition. Furthermore, derivatives of these low molecular weight oligomers (such as esterified products of the oligomers with diazonaphthaquinone compounds) are themselves photoactive and can be used in a photoresist composition. As such, the present invention also provides a process for producing a photoresist composition comprising said low molecular oligomers or derivatives of said low molecular weight oligomers. The present invention also provides a process for producing a semiconductor device by forming an image on a substrate utilizing the foregoing low molecular oligomers or their derivatives.
Fractionation reduces the overall yield of a resin by removing low molecular weight materials (such as unreacted monomers, dimers, trimers and intermediate oligomers). Depending upon the functional properties needed for the final resist, many fractionation techniques can be devised for the general removal of a broad range of these lower molecular weight fractions and intermediate oligomers. Economically, the cost of the raw material is directly related to the yield of useful resin obtained from the fractionation steps. It would be desirable to selectively remove those fractions that are known in a particular technical application to affect functional properties of a final resist composition without substantial lowering the overall yields of the film forming resin. The present invention affords such a process for selective removal of oligomeric fractions of a film forming resin. For example, in the preparation of microelectronic devices, multiple high temperature baking steps may be used to a) remove solvents immediately after spin coating the liquid resist composition onto a semi-conductor substrate and a post development bake after the wafer is imaged through a photomask. Other heat treatment steps may be optionally applied to further remove entrained solvents or to facilitate heat activated chemical changes in the coated film. Serious defects can occur in some of these heat treatment steps when low molecular weight oligomers of a film forming resin, such as dimers and trimers of a novolak resin, volatilize, and either affect film integrity or, more commonly, sublime on the inside of the processing equipment. It would be desirable to remove substantial portions of the low molecular oligomers of a film forming resin, such as dimers/trimers of a novolak resin, while retaining a high yield of the remaining film forming resin. The present invention affords a method for the selective removal of such dimers and trimer fractions of the film forming resin. While distillation methods can be used to remove volatile materials such as low molecular weight oligomers, these methods are batch processes and require long set-up times and cleaning steps, and the yield of the resulting fractionated resin is also low. These disadvantages are lacking in the present invention. In the present invention, by the combined use of a static mixer and liquid/liquid centrifuge fractionation process, one can continuously remove low molecular weight oligomeric fractions, such as dimers and trimers of a film forming resin, while maintaining a high yield of the desired fractionated film forming resin.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of a film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.
There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered.
After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etch that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate and its resistance to etching solutions.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less than one micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate.
U.S. Pat. No. 6,121,412 and International Publication WO 00/33137 disclose a method for producing a film forming, fractionated novolak resin, by: a) condensing formaldehyde with one or more phenolic compounds, and thereby producing a novolak resin; b) adding a photoresist solvent, and optionally a water soluble organic polar solvent; c) feeding the mixture into a liquid/liquid centrifuge and feeding a C5-C8 alkane, water or aromatic hydrocarbon solvent into the liquid/liquid centrifuge at a ratio of optional water-soluble organic polar solvent and photoresist solvent to C5-C8 alkane, water or aromatic solvent, of from 5:1 to 0.5:1; d) rotating the liquid/liquid centrifuge containing the mixture at a speed of at least 500 rpm and thereby separating the mixture into two phases, collecting the two phases; e) optionally separating the lighter phase (L) into two second phases; f) removing residual C5-C8 alkane, water or aromatic hydrocarbon solvent from the heavier phase (H) from step d) and leaving the novolak resin dissolved in the photoresist solvent. A method is also provided in these references for producing photoresist composition from such a fractionated novolak resin and for producing microelectronic devices using such a photoresist composition.
The present invention provides a method for separating and isolating low molecular weight oligomers of a film forming resin, said method comprising:
c) providing a solution of the film forming resin in a first solvent system comprising a photoresist solvent, and optionally a water-soluble organic polar solvent, wherein the ratio of the photoresist solvent to the water soluble organic polar solvent ranges from about 10/90 to about 100/0;
b) providing a second solvent system comprising at least one substantially pure C5-C8 alkane and/or at least one alkyl aromatic compound having at least one hydrocarbyl substituent and/or water/C1-C4 alcohol mixture provided that the C1-C4 alcohol content of the water/C1-C4 alcohol mixture is less than 50% by weight; and performing steps c)-e) below in the following order:
c) mixing the solutions from a) and the second solvent system from b) in a static mixer for a time period sufficient for efficient mixing;
d) feeding the mixture from c) and the second solvent system from b) through two separate inlet ports into a liquid/liquid centrifuge, one of said inlet ports feeding the mixture from c), the second inlet port feeding the second solvent system from b) into said liquid/liquid centrifuge at a feed ratio of the mixture from c) to the second solvent system from b) of from about 10/90 to about 90/10, at a temperature of from about 0xc2x0 C. up to a maximum temperature that is less than the boiling point of the lowest boiling solvent in the first or second solvent system;
e) rotating the mixture from step d) inside the liquid/liquid centrifuge at a rotational speed sufficient to separate the mixture from step d) into two separate phases, and then collecting the two separate phases, each from two separate outlet ports, into two separate containers, wherein the heavier phase (H) comprises higher molecular weight fractions of film forming resin, in the first solvent system with a minor amount of the second solvent system, and the lighter phase (L) comprises low molecular weight oligomers of the film forming resin in the second solvent system with a minor amount of the first solvent system.
The present invention also provides a method for producing a photoresist composition, said method comprising: providing an admixture of: 1) a fractionated film forming resin comprising higher molecular weight fractions of the film forming resin, said fractionated film forming resin produced according to the aforementioned method; 2) a photosensitive component in an amount sufficient to photosensitize a photoresist composition; and 3) an additional photoresist solvent to form the photoresist composition.
The present invention also provides a method for producing a photoresist composition, said method comprising: providing an admixture of 1) a film forming resin; 2) a photosensitive component in an amount sufficient to photosensitive the photoresist composition; 3) a speed enhancing composition comprising low molecular weight oligomers of a film forming resin made by the aforementioned method; and 4) a photoresist solvent; to form the photoresist composition.
The present invention further provides a method for producing a photoresist composition, comprising: providing an admixture of: 1) a film forming resin; 2) a photosensitive component in an amount sufficient to photosensitize the photoresist composition, said photosensitive component comprising an ester made by reacting the low molecular weight oligomers of a film forming resin having reactive hydroxyl groups, said low molecular weight oligomers made by the aforementioned method, with a diazonaphthoquinone sulfonyl chloride; and 4) a photoresist solvent; to form the photoresist composition.
The present invention also provides a method for producing a microelectronic device by forming an image on a substrate, said method comprising: a) providing any of the aforementioned photoresist compositions; b) thereafter, coating a suitable substrate with the photoresist composition from step a); c) thereafter, heat treating the coated substrate until substantially all of solvent is removed; image-wise exposing the coated substrate; and then removing the imagewise exposed or, alternatively, the unexposed areas of the coated substrate with a suitable developer.